Under fire during question period in the House of Commons, Alexander denounced Galati — the same lawyer who successfully challenged the appointment of Marc Nadon to the Supreme Court of Canada — as the "disgraced ideological former lawyer of the Khadr family."

That was a reference to Galati's brief stint representing Abdurahman Khadr, a former Guantanamo Bay detainee whose younger brother Omar was convicted of war crimes in the death of a U.S. sergeant in Afghanistan in 2002.

A group of lawyers led by Galati is taking on Bill C-24 as unconstitutional, in particular those provisions that would let the government revoke citizenship from dual nationals — even if they are born in Canada.

NDP multiculturalism critic Andrew Cash was among those leading the opposition charge against C-24 on Tuesday, denouncing it as just the latest Conservative effort to circumvent the Constitution.

"Let us enumerate: a Supreme Court pick, rejected; the crime bill is overturned; the Senate reform proposal, ruled unconstitutional; and that was just the spring session," Cash railed.

"Mr. Speaker, that question speaks to the pitiful quality of opposition criticism and commentary throughout this debate on Bill C-24," Alexander shot back.

"We will stand behind a bill if the main opponent to it is the disgraced ideological former lawyer of the Khadr family."

Alexander defended the bill in the House, insisting the government already has the power to revoke citizenship when it has been "fraudulently obtained."

"Under the new act, we would have the power to revoke it when someone has refused to reveal that they committed crimes, that they committed human rights abuses, that they committed war crimes," he said.

"And yes, Canadians find it entirely acceptable that we should revoke the citizenship of dual nationals for terrorism, spying or treason."

In an interview later on CBC's Power and Politics, Galati fired back at Alexander, accusing him of making disparaging remarks while hiding behind the protection of privilege that comes on the floor of the Commons.

"It's absolutely pathetic the things he says in the House when it's covered by parliamentary privilege," he said.

"I don't have to defend my reputation as a constitutional lawyer; my record speaks for itself. He should look at the substance of the arguments, not who he thinks I am or am not."

It's not Galati's first time sparring with the Conservative government.

In October, he launched a constitutional challenge of Prime Minister Stephen Harper's attempt to appoint Nadon, a semi-retired Federal Court of Appeal judge, to one of three seats on the high court reserved for Quebec.

Six months later, the court agreed, saying Nadon was ineligible under the Quebec-specific provisions of the Supreme Court Act.

On Monday, Galati wrote to members of Parliament, senators and Gov. Gen. David Johnston, saying he and other lawyers were "alarmed" by provisions contained in the legislation.

"Our challenge is restricted to the narrow issue of whether or not this Parliament has the constitutional authority to strip the citizenship of a Canadian-born; we're not looking at any other provision in this law," he told CBC.

"They're acting completely outside of the Constitution in a renegade, reckless and flagrant manner, and they know it."

The bill was expected to pass through the Commons quickly after the Conservatives used their majority Monday to limit debate.

The Canadian Bar Association's national law immigration section warned in April that the legislation raised "serious human rights concerns." Lawyers with the association are scheduled to appear Tuesday before a Senate committee to reiterate their concerns.

Galati has said he plans to apply for a judicial review with the Federal Court by next week if he does not receive a response from the government or the Governor General.